Structural characterization of flavonol 3,7-di-O-glycosides and determination of the glycosylation position by using negative ion electrospray ionization tandem mass spectrometry

Flavonol 3,7‐di‐O‐glycosides were investigated by negative ion electrospray ionization tandem mass spectrometry using a quadrupole linear ion trap (LIT) mass spectrometer. The results indicate that the fragmentation behavior of flavonol 3,7‐di‐O‐glycosides is substantially different from that of their isomeric mono‐O‐diglycosides. In order to characterize a flavonoid as a flavonol 3,7‐di‐O‐glycoside, both [Y30 − H]−• and [Y0 − 2H]− ions should be present in [M − H]− product ion spectrum. The MS3 product ion spectra of Y30−, [Y30 − H]−• and Y70− ions generated from the [M − H]− ion provide sufficient structural information for the determination of glycosylation position. Furthermore, the glycosylation positions are determined by comparing the relative abundances of Y30− and Y70− ions and their specific fragmentation patterns with those of flavonol mono‐O‐glycosides. In addition, a [Y30 − H]−• ion formed by the homolytic cleavage of 3‐O glycosidic bond with high abundance points to 3‐O glycosylation, while a [Y0 − 2H]− ion formed by the elimination of the two sugar residues is consistent with glycosylation at both the 3‐O and 7‐O positions. Investigation of negative ion ESI‐MS2 and MS3 spectra of flavonol O‐glycosides allows their rapid characterization as flavonol 3,7‐di‐O‐glycoside and their differentiation from isomeric mono‐O‐diglycosides, and also enables their direct analysis in crude plant extracts. Copyright © 2006 John Wiley & Sons, Ltd.